Category Archives: Digital Voice

Searching for some FreeDV QSO partner on VHF

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Since i use Quisk for my HiQSDR i found it interesting to experiment with FreeDV again. Quisk can directly support using the FreeDV API and work in this digital mode without building lots of cables. Since i wanted to try the latest mode 700C i had to compile the library from the scratch and add the mode to the configuration of quisk. Below you can find recordings of my CQ call in the modes 1600 and 700C which were made loopback.
Now i search for a QSO partner preferably on 2m somewhere in the area around JO61. I can work relatively well direction southeast. So east OK might be good.

Mode 1600

Mode 700C

Please remember the 700C mode uses only 1kHz of bandwidth.
If you are interested in some tests just send me a email to dh5ym@darc.de

MD380 DMR radio

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I have a Tytera MD380 DMR transceiver now. Flashed latest MD380tools and database yesterday and hope to make a first qso soon. A mmdvm hotspot is in the pipeline but i still need to connect a transceiver.

TYT MD380 DMR radio

IC-E92 spectrum

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Triggered by some forum discussion about interference risk of operating repeaters in neighbor channels in 6.125kHz channels I was curious about the TX spectrum of my IC-E92. The measurement was done radiated. I checked for neighbor channel interference. You can see the delta values bottom right.

FM wide:

IC-E92 FM wide 1750Hz

IC-E92 FM wide 1750Hz

FM narrow:

IC-E92 FM narrow 1750Hz

IC-E92 FM narrow 1750Hz

D-Star (only half span screenshot):

IC-E92 D-Star

IC-E92 D-Star

You can see that D-Star is really the most narrow band mode. Using neighbor frequencies at close QTH still cannot be suggested but at least the interference will be less than for narrow band FM.

Freedv / FDMDV2 – digital voice shortwave

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Since a long time David Rowe VK5DGR works on a open-source low-rate voice codec. This project is called codec2.
Now a variant of this codec is used in a amateur radio digital voice mode that was evolved out of the well known FDMDV software.
The mode uses OFDM with 14 carriers DQPSK and 2 pilot carriers with twice the power modulated in DBPSK.
The bandwith is 1kHz, so 2 of the signals would fit to 1 SSB channel. The datarate of the voice is 1375 Bit/s + some data bits for callsign information etc.
Its intended that in the end this mode can also be used for DX connections. Lets see what live tests will bring. On 20m obviously the frequency 14.236MHz is used as center of gravity.
For using the mode you would need either a two-soundcard PC (one for connecting a headset and one for creating the digital modulation signal) or a SDR setup with virtual soundcards. Currently a windows beta release can be downloaded as binary. For Linux you have to download the source and compile it on your own. David created a nice Makefile that downloads and compiles all dependecies.
You find further information on the project page http://freedv.org/tiki-index.php.
Also some videos are linked that show the operation and the audio quality of this digital mode.

some experiments with FreeDV and Quisk

some experiments with FreeDV and Quisk

How the digital signal of Freedv/FDMDV2 sounds like:
freedv-test

How the decoded audio sounds like (its only 1375bit/s with 1kHz bandwidth!):
REC-0003

D-Star / Digital Voice activities

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This week i got the new DVRPTR pcb. (see www.dvrptr.de)
Connected to a Windows or Linux PC it is easy to create a hotspot for connecting to D-Star Reflectors ans X-Reflectors. From time to time i am running a hotspot on 430.225MHz from my home location in the east of Dresden (Just when i am at home). Probably someone can hear it. It is usually connected to XRF010B.

D-Star under impulse noise conditions

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Last week DL3OCK generated a testfile for me. This file contains an FM signal and an D-Star signal with 50kHz offset. It can be transmitted with special equipment. I used this to check the behavior of my C5 70cm transceiver close to noise level and with impulsive noise. Find the videos below.

http://www.youtube.com/v/0Zz1Qd5ch4A

This video shows the comparison between D-Star and FM at around -115dBm.
It is clearly audible that D-Star has some advantages against FM if the decoder can stay in sync. The microphone of the camera does not represent the FM very well. In reality the FM sound was slightly better.

http://www.youtube.com/v/0mD1gWB2B58

This video shows the performance of FM vs D-Star under impulsive noise conditions. It is clearly audible that D-Star works without problems when FM is hard to understand.